Rear shock spring replacement/upgrade??

It has been a while since I've visited here but now I'm looking for some help with my rear shock. My 84 VF1000F has a CBR 600 f3 rear shock that has a stock spring and I have searched for a replacement spring with the proper rating but can't seem to determine what I need? Every place I look wants me to use a rate calculator to choose a spring but I know that dosent apply due to bike weight, linkage geometry and rider weight distribution. The bike handles ok solo but I have the preload at the highest setting, riding 2-up it sags a good 3 to 4 inches. So I guess the questions are (1) what calculations should I use? (2) where is the best place to buy a spring? Thanks for any help!!

 

If I was in your shoes, I'd go ask this dude (Jamie) , probably one of the best, if not the best in this field. http://www.daughertymotorsports.com/

 

What he said ^^^^^^
Jamie's the master


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yupp +1 for jamie

 

I'll check with him, thanks!

 

He's doing one for me right now -- same problem, my current setup is undersprung for a 210 lb rider.

He's super helpful, and knows these bikes.